Heterogeneous networks arose due to the rapid increase of numbers of mobile subscribers and demand for bandwidth, and the inadequacy of traditional macro base stations in meeting subscriber requirements. Homogenous networks consisting of solely traditional macro base stations may have blind spots in coverage that adversely impact user experience. With the introduction of lower power base stations, including pico cells, femto cells, and relay nodes, newer generation of wireless network topology such as that of a LTE-A network becomes a heterogeneous network (HetNet) that is able to deliver more complete coverage and to support diverse types of wireless devices. In a HetNet as defined in 3GPP, low power nodes (LPNs), such as RRU/RRH, pico eNB (Enhanced Node B), home eNB, and relay node, are deployed inside or next to the macro base station or enhanced node B coverage cell.
One consequence related to the heterogeneous network deployment where small-power nodes are being placed in a high-power macro-cell layout is an uplink (UL) power imbalance caused by the transmit power difference between the small power nodes and macro-cell. Simulation results illustrate three potential problems arising from the uplink power imbalance: (1) unreliable HS-DPCCH decoding at the serving cell; (2) excessive UL interference from the macro-cell to low power node; and (3) excessive UL interference from the low power nodes to a macro cell. Similar issues could be expected for LTE HetNet, i.e., unreliable PDCCH decoding, and excessive UL interference from both macro or pico nodes. Various coordination techniques have been proposed for dealing with this interference in LTE specifications such as feICIC, however these may not be used in all networks since time domain interference coordination creates a requirement that the aggressor and victim cell are synchronized. Therefore, it is desired to have a measurement and reselection mechanism that can take into account the pathloss between the UE and a macro cell and between the UE and a pico cell in order to minimize or avoid interferences.
The following abbreviations are used in this application.
AIL Acceptable Interference Level
BS Base Station
CPICH Common Pilot Channel
CRE Cell Range Expansion
DL Downlink
DPCCH Dedicated Physical Control Channel
E-DCH Enhanced Data Channel
EUTRAN Enhanced UTRAN
eICIC Enhanced Inter-Cell Interference Coordination
eNB Enhanced Node B.
FDD Frequency Division Duplex
HS-DPCCH High Speed-Dedicated Physical Control Channel
LP Lower Power
LTE Long Term Evolution
OAM Operation, Administration and Maintenance
PDCCH Physical Downlink Control Channel
PDSCH Physical Downlink Shared Channel
PRB Physical Resource Block
RCC Radio Resource Control
RLC Radio Link Control
RNTP Relative Narrowband Tx Power
RRC Radio Resource Control
RSRP Reference Signal Receiving Power
RSRQ Reference Signal Received Quality
RRU/RRH Remote Radio Unit/Remote Radio Head
Rx Receive
RSCP Received Signal Code Power
RSSI Received signal strength indicator
TDD Time Division Duplex
Tx Transmit
UE User Equipment
UMTS Universal Mobile Telecommunications System
UTRAN UMTS Radio Access Network
WCDMA Wideband Code Division Multiple Access